Electrodeposition of Mo/Zn/Cu/Sn Unconventional Stack for CZTS Thin Films Synthesis

Abstract

The interest towards Cu2ZnSnS4 (CZTS) photoactive material relies into the abundancy and non-toxicity of the elements considered [1, 2]. Among the fabrication routes investigated in literature, the single layer approach, consisting in the electrodeposition of Cu, Sn, Zn layers followed by reactive annealing, is the most promising showing higher efficiency devices than coelectrodeposition-based ones. The typical stack order is Mo/Cu/Sn/Zn, where the electrodeposition of the most noble metal is followed by intermediate and subsequently by the least noble one [2, 3]. This layer sequence is strongly connected to water-based electrolytes where pH dependence limits the possible stack combinations. However, it was reported that the ideal layer stacking, fabricated by means of sputtering, would consider to have Zn as first layer to avoid its loss during the annealing treatments (high vapor pressure) and to promote a good interface with Mo [4]. In the present work, a traditional electrodeposition-annealing route of an unconventional stack order (Mo/Zn/Cu/Sn) is proposed by employing an organic solution based on ethylene glycol for the copper electrodeposition while an aqueous one for zinc and tin depositions. The electrochemical behaviour of the copper solution was investigated by means of cyclic voltammetry (CV) and linear sweep voltammetry. Galvanostatic approach was investigated, employing of Hull cell as preliminary test. Soft and reactive (sulfur atmosphere) annealing were performed; the formation of kesterite were verified by means of Raman spectroscopy. CZTS thin films were characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD); photoelectrochemical characterization was performed to evaluate the photoactivity.